Takayasu's arteritis is a chronic inflammatory condition that affects the aorta, the largest blood vessel in the body, and its branches. Inflammation causes segments of the vessels to become narrowed, blocked, or even stretched, possibly resulting in aneurysms. The disease is very rare but most commonly occurs in young Asian women. Symptoms may include arm pain with use, decreased or absent pulses, lightheadedness or dizziness, headaches, and visual disturbances. Many individuals with Takayasu' arteritis, however, have no apparent symptoms despite disease activity. Additionally, current tests used to measure vessel inflammation are considered unreliable and inconsistent. It is therefore very difficult to determine the extent of disease activity in a person with Takayasu's arteritis. This study will use novel scientific methods to establish new biomarkers that can be used to monitor disease activity in individuals with Takayasu's arteritis. These biomarkers may be used to help direct clinical care and assist in future drug development.